Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit) Recognized in Net Periodic Benefit Cost, before Tax	$ (34.0)	$ (31.9)
Document Period End Date	Dec. 31, 2014
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	(56.7)	71.6	30.8
Accumulated Other Comprehensive Income (Loss), Net of Tax	(3,991.8)	(2,002.7)
Other comprehensive income (loss)	(1,989.1)	1,794.4	61.5
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax	269.0	483.3
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax	303.0	515.2
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Tax	(83.4)	(164.3)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax	185.6	319.0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	(324.1)	(12.0)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, before Tax	0	2.4
Other Comprehensive Income (Loss), Reclasification Adjustment from AOCI, Available-for-Sale Securities, before Tax, Total	(324.1)	(9.6)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	113.4	3.4
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Available-for-Sale Securities, Net of Tax, Total	210.7	6.2
Other Comprehensive Income, Other, Net of Tax	5.9	5.9
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(19.2)	318.7
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	5.2	43.2	(2.8)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, before Reclassification Adjustments, Tax	414.7	(886.1)	(34.4)
Other Comprehensive Income (Loss), Tax	476.6us-gaap_OtherComprehensiveIncomeLossTax	(914.5)us-gaap_OtherComprehensiveIncomeLossTax	(68.0)us-gaap_OtherComprehensiveIncomeLossTax
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(3,991.8)	(2,002.7)	(3,797.1)	(3,858.6)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	1,969.9	(1,475.7)
Other comprehensive income (loss)	(1,989.1)	1,794.4	61.5
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	19.2	(318.7)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(498.4)	463.0	426.8	265.9
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	961.4	(36.2)
Other comprehensive income (loss)	(961.4)	36.2	160.9
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	99.7	205.2	72.5	14.8
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(105.2)	(138.9)
Other comprehensive income (loss)	(105.5)	132.7	57.7
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax			104.1
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	210.7	6.2
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax			(46.4)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(3,402.0)	(2,489.1)	(4,195.2)	(4,032.2)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	1,098.5	(1,387.1)
Other comprehensive income (loss)	(912.9)	1,706.1	(163.0)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(185.6)	(319.0)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(191.1)	(181.8)	(101.2)	(107.1)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	15.2	86.5
Other comprehensive income (loss)	(9.3)	(80.6)	5.9
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax			0
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax			(5.9)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ (5.9)	$ (5.9)

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